High-speed photographic or cinematographic varifocal objective



SEARCH ROOM G. KLEMT ETAL HIGH-SPEED PHOTOGRAPHIC OR CINEMATOGRAPHIC VARIFOCAL OBJECTIVE Filed Feb. 11, 1960 MM5 Ei Karl MCHER Q izan Agent United States Patent O 3,057,257 HIGH-SPEED PHOTOGRAPHIC OR CINEMATO- GRAPHIC VARIFOCAL OBJECTIVE Gnter Klemt and Karl Macher, Kreuznach, Rhineland, Germany, assignors to Jos. Schneider & Co., Optische Werke, Kreuznach, Rhineland, Germany, a corporation of Germany Filed Feb. 11, 1960, Ser. No. 8,069 Claims priority, application Germany Feb. 17, 1959 2 Claims. (Cl. 88-57) Our present invention relates to varifocal objectives for photographe or cinematographic cameras.

It is known to assemble a varifocal objective system from a principal or basic objective of fixed focal length and an associated front attachment Whose focal length is adjustable. Such attachments advantageously include a fixed front component on the object side of the system, a fixed rear component on the image side of the system, i.e. next to the basic objective, and one or more movable components between the two fixed components. Varifocal attachments of -this general description have the advantage of a constant physical length and afford greater convenience in the mounting of the movable lens supports since only the smaller intermediate component or components need to be displaced, the large front component remaining stationary. With two negatively refracting movable cornponents between two fixed outer components of positive refractivity, the displacement of these movable compo-- nents can be made to approach a linear function of the adjustable focal length so that the need for a complex control mechanism, involving cams or the like, is eliminated.

The general object of our present invention is to provide a varifocal system of this character in which the various aberrations inherent in such systems are reduced to a minimum.

More specifically, it is an object of this invention to provide a varifocal system in which the residual aberrations are substantially constant throughout the range of adjustment so that compensation thereof in the'design of the basic objective becomes possible.

In accordance with the present invention we realize the above objects by making the focal length of the fixed positive rear component equal to or less than 75% of the focal length of the fixed positive front component while making the focal length of the more rearward movable negative component larger by at least than that of the more forward movable negative component. Advantageously, in order to reduce the total axial dimension of the system, we make the focal length of the aforementioned positive rear component larger than the sum of the three air spaces separating the two movable components from each other and from the two positive components, this sum remaining of course constant under all conditions of operation.

In a preferred embodiment, in which the fixed front component consists of two air-spaced lens members of which the second one as well as each of the other three components may be cemented, we design the two movable components in'such manner that respective concave outer surfaces thereof, more strongly curved than their other surfaces, face each other across the intervening variable air space. The radii of curvatiure of the other surfaces (including the cemented ones) of these movable compoice nents are preferably considerably larger than those of the two concave surfaces referred to.

The invention will be described in greater detail with reference to the accompanying drawing in which:

FIG. 1 shows a varifocal system according to the invention in a position of adjustment for minimum focal length (f=50);

FIG. 2 shows the same system in a position of adjustment for an intermediate focal length (fr-); and

FIG. 3 shows the system adjusted to maximum focal length (f=200).

The system shown in the drawing comprises a varifocal attachment, consisting of four components I-IV, and a fixed principal or basic objective designated component V. The fixed front component I, of positive refractivity, consists of a nearly plano-convex singlet L1 (radii r1, r1 and thickness d1 and, separated from it by a small air space d2, of a doublet composed of a positive lens L1 (radii r3, r4 and thickness d3) and a negative lens La (radii r1, rs and thickness d4). A variable air space d5 separates front component I from the first intermediate component II, of negative refractivity, which consists of a positive lens L1 (radii r6, f7 and thickness d6) and a negative lens L5 (radii r1, r1, and thickness dq). Another variable air space da marks the distance of the vertex of the more strongly concave surface (rs) of component II from the corresponding surface (r9) of the second intermediate, negatively refracting component III which consists of a negative lens L6 (radii r9, r11, and thickness dg) and a positive lens L, (radii r10, r11 and thickness d10). Component III is separated by a variable air space d11 from the fixed positively refracting rear component IV which consists of a positive lens L8 (radii r12, r13 and thickness du) and a negative lens L9 (radii r13, r1.1 and thickness d13).

The two intermediate components `II and III are displaceable between their extreme positions, illustrated in FIGS. l and 3, to change the focal length of the attachment I-IV and, therefore, of the overall objective system I-V. It will be understood that this change in focal length will be accompanied by only negligible shifts in backfocal distance so that the position of the image plane of the system, coinciding with the surface of a lm or other photosensitive element, will remain substantially unchanged.

The unit I-IV is separated by an air space d14 from the basic objective, component V, consisting of four airspaced singlets L10-L13. Biconvex lens L10, having radii r15, r11; and thickness d15, is spaced by a small distance d1@ from positive meniscus L11 having radii r11, r11, and thickness d17; there follows, beyond an air space dw, the biconcave lens L12 with radii r11), rm and thickness 4119, the final air space d20 separating thislens from the biconvex lens L13 with radii r21, r22 and thickness e121.

Representative numerical values for the radii r1 to rzz and the thicknesses and separations d1 to d21 of lenses L1 to L13 will be given in the following table, based upon the median overall focal length f=l00 of the system adjusted as in FIG. 2; the values listed for the variable air spaces d5, da and d11 refer also to the position of FIG. 2. The table further gives the refractive indices nd and the Abb numbers v of these lenses along with the total physical length :110181 of the system and the individual focal lengths f1, f2, f3, f1 and f5 of the components I-V.

Tlilcknesses and i111' spacings Lens Radii v n 342. 55 di 20.00 1.52542 64.55

dq 0.40 Air space I r; 287.20 f,=-|-424.0 LL.-- di 19.35 1.62041 60.29

r4 =4, 232. 50 Lsdi 5.85 1. 70182 26. 52

da =124. 25 lAir space f5 B50. 50 L4-.-- de 10.25 1.75520 27. 53 II r1 231.95 fi=191.0 175--.- di 3.10 1.50378 66.73

ra =l 93.15 dg 34.10 lAirspace n 118.15 LL.-- dv 2.95 1.50378 66.73 III r=+ 141. 25' =219.0 L1- dio 7. 30 1.75520 27. 53

d 64.70 IAir space m=| 307.65 Li---- dii 6.85 1.62041 60.29 IV ria= 104. fi=+242.0 LL--- di; 3.40 1.62004 36.34

dii 45.00 Airspace f15=+ 64.95 Lm--- di; 10.20 1.62041 60.29 fi6=1,050.00

d 0.15 Airspace i n1=+ 38.93

Tig=+ 49. 55 V 1 dm 6.80 Air space 91.34 f9=' 29.90 f5 1....-.- a.. 2. 85 1.59595 so. 05

d10 13.75 Airspace Tzi=+ 93. 40 LIL.-- dii 10.85 1.65830 57. 29

dtutnl=402.

l Variable.

As will be seen from the foregoing table, the constant sum of the three variable air spaces d5, d8 and du equals 223.05, being thus less than the focal length f4 which in tiirn is less than 75% of the focal length f1. Focal length f3 exceeds focal length f2 by more than 10%.

The objective system represented by the table has an aperture ratio of 1:2.8 and a varifocal ratio of substantially 1:4 as given by the minimum focal length f=50 (FIG. l) and the maximum focal length f=200 (FIG. 3).

We claim:

1. A varifocal attachment for an optical objective, consisting of four components separated from one another by variable aii" spaces, said components including a fixed front component of positive refractivity, a first movable intermediate component of negative refractivity, a second movable intermediate component of negative refractivity and a xed rear component of positive refractivity, said rear component having a focal length equal to at most 75 of the focal length of said front component, said second intermediate component having a focal length exceeding by at least 10% the focal length of said rst intermediate component, the sum of said air spaces being less than the focal length of said rear-component, the absolute values of the focal lengths of said front. rst intermediate, second intermedi-ate and rear components being related to one another substantially in the proportions 424: 191 :219:242, the radii r1 to r1.1 and the thicknesses and separations d1 to dla of the lenses L1 to L9 forming part of said front component Lsaid first intermediate component II, said second intermediate component III and said rear component IV, their indices of refraction nd and their Abbe numbers v having numerical values substantially as given 1n the following table:

Thicknesses and air spacings Lens Radii u 'lld n=+ 342.55 L, d. 20.00 1. 52542 e4. 55

dz 0.40 Airspace I r3=+ 287.20

r. =-4, 232. 50 La di= 5.85 1.75192 25.52

d; =124. 25 1 Air space r.. 850.50

ds 34.10 lAir space rg 118.15 L. d= 2.95 1.50378 55.73 111 m=+ 141.25

L7 dw= 7.30 1.75520 27.53

d|1= 64.70 l.Air space m=+ 307. 55 f La du= 6.85 1. 5204i 60. 29 IV m= 104. 15

lVariable.

2. The combination of an attachment according to claim 1 with a basic objective consisting of four airspaced singlets L10 to L13 whose radii r15 to 722, thicknesses and separations d15 to dm, indexes of refraction nd and Abb numbers 11, together with the air space du between said attachment and said basic objective, have numerical values substantially as given in the following table:

Tllicknesses and air spacings Lens Radii u di4=45. 00 Air space Ti5=+ 54.95 Lm d15=10. 20 1.62041 60. 29

dm= 0.15 Air space r17=+ 38. 93 L11 d17=10. 10 1. 62041 60. 29

d|9= 6.80 Air space r19= 129. 9() L11 d19= 2.85 1.69895 30.05

rzo=l 33.20

d10=13. 75 Air space rzi=+ 93.40 L13 du =10. 85 1. 65830 57. 29

References Cited in the file of this patent l UNITED STATES PATENTS 2,514,239 Hopkins June 4, 1950 2,746,350 Hopkins May 22, 1956 2,844,996 Klempt July 29, 1958 Angenieux 2---- Aug. 19, 1958 

